Apparatus for gas-liquid mixing is used for many chemical reaction processes and fermentation processes. A liquid to be reacted is placed in a reactor vessel. The liquid contains compounds to be reacted or cells which take part in a fermentation process. A gas is introduced into the liquid by a variety of techniques, and a reactive component of the gas reacts with the liquid in a desired manner.
One objective in the operation of gas-liquid reactors is a high rate of reaction in order to reduce processing times and costs. High reaction rates are obtained by increasing the interface area between the gas and the liquid which requires a large number of very small gas bubbles distributed through the liquid. It is well-known that a given volume of gas has maximum surface area when it is subdivided in a large number of small bubbles. In order to transfer large gas volumes to a liquid in the required form of evenly distributed small bubbles, energy must be applied to the liquid as a shear force. A large fraction of the energy used for stirring or agitation of the liquid by rotary mixers is not available as a shear force for gas-liquid mixing. In addition, small bubbles in the liquid have a tendency to coalesce into larger bubbles and rise to the surface, limiting the gas-liquid interface area and causing a pressure buildup in the head space at the top of the vessel.
A variety of techniques has been used for gas-liquid mixing including mechanically agitated tanks, sparged gas columns and nozzle assemblies to disperse gas in a liquid. One widely used gas-liquid reactor includes a submerged jet nozzle at the bottom of a cylindrical vessel, and a guide tube coaxial with the cylindrical vessel and positioned over the submerged jet nozzle. A gas-liquid mixture, injected by the nozzle, circulates upwardly through the guide tube to the surface of the liquid and then downwardly in the annular space outside the guide tube, resulting in continuous circulation. In another prior art gas-liquid reactor, a so-called free jet nozzle is positioned at the top of a vessel in the head space above the liquid surface. Reactive gas is introduced into the head space and is entrained by the downwardly injected liquid jet from the free jet nozzle.
All of the prior art gas-liquid reactors suffer from certain deficiencies and disadvantages. The gas introduced into the liquid tends to coalesce into larger bubbles and rise to the surface of the liquid, thereby reducing the interfacial surface area between the gas and the liquid. The unreacted gas in the head space must be vented to maintain system pressure and may be lost from the system. Usually the gas vented from the head space is only partially reacted and still contains useful reactive components. A variety of baffles, guides and tubes have been incorporated into reactor assemblies to extend the path length of the gas-liquid mixture and to provide more time for gas and liquid to be in intimate contact. However, none have been totally satisfactory. As a result, prior art reactors have been relatively inefficient in transferring gas to the liquid for reaction. Relatively large amounts of energy have been required to transfer limited amounts of gas to the liquid.
It is a general object of the present invention to provide a novel gas-liquid reactor.
It is another object of the present invention to provide a novel gas-liquid reactor with a high gas transfer rate.
It is a further object of the present invention to provide a novel gas-liquid reactor utilizing a submerged jet nozzle and at least two free jet nozzles to achieve a high rate of transfer of gas to the liquid.
It is a further object of the present invention to provide a novel gas-liquid reactor with relatively low energy requirements for transferring the gas to the liquid phase.
It is a further object of the present invention to provide a novel gas-liquid reactor wherein gas is efficiently transferred to the liquid phase.
It is a further object of the present invention to provide a method for effectively transferring a reactive gas to a liquid in a gas-liquid reactor.